June Newsletter

Equine Herpesvirus

Youíve probably been hearing a lot about Equine Herpes Virus (EHV) lately.
Recently there was an outbreak of EHV at the National Cutting Horse Association (NCHA) Western National Championships, held April 29 through May 8 in Ogden, Utah. There were over 400 horses stabled at this show.  The show concluded and these horses all went back home. These horses came from 19 different states and Canada. Shortly after the conclusion of the show several horses developed clinical signs consistent with Equine Herpesvirus Myelitis (EHM). Many of the sick horses were transported to University hospitals. Due to the contagious nature of this disease the hospitals were closed to incoming cases until the danger had passed. Many shows and events were cancelled due to fear about the spread of the virus.
Weíve had a large number of phone calls and emails with questions about this outbreak and have also seen a tremendous amount of false information being spread particularly through the internet. So, Iíd like to share some information with you about the virus, the disease and steps that you should take to protect your horse.

About the virus
  • Equine Herpes Virus (EHV) is not new; itís been around for as long as records have been kept.
  • EHV belongs to the Herpesvirus family. EHV affects horses only, you cannot get EHV from your horse. There are human strains of herpes virus and these strains do not infect humans. Chicken Pox is caused by a herpes virus. You cannot give Chicken Pox to your horse. Your horse cannot give you Equine Herpes virus.
  • Most herpes viruses are highly contagious, if you have ever had children you know how fast the Chicken Pox ran through the class of first graders! Herpesvirus in horses is also highly contagious among horses.
  • Herpesviruses like to become dormant and hibernate within the hostsí body only to become active later on, this is called latency. In humans the Chicken Pox virus lies dormant in our bodies and can resurface many years later in the form of Shingles. Herpesvirus can lie dormant in horses only to become active when a horse is under stress and the immune system is compromised. Hauling, competition and illness are all common triggers for EHV to become active.
  • There are seven (7) strains of EHV labeled as EHV-1, EHV-2 etc. As horse owners we are primarily concerned with EHV 1 and 4.
  • EHV-1 is the most virulent strain of equine Herpesvirus. Virulence refers to the ability to cause disease. EHV-1 is capable of causing respiratory disease, abortion and neurologic disease. EHV-4 usually causes respiratory disease only but can occasionally cause abortion.
  • Most horses become infected with EHV-4 as weanling and yearlings. They may show nasal discharge and a low grade fever but most recover without treatment.

Why is EHV-1 such a problem?
  • EHV-1 has the ability to attack endothelial cells. Endothelial cells are cells that line the blood vessels. Healthy endothelial cells keep blood flowing within the vessel where it is supposed to be. Itís kind of like a swimming pool liner, if the liner is leaking the pool starts to leak. Imagine that the virus attacks the endothelial cells of the placenta in a pregnant mare. The placenta starts to leak and the mare aborts. Likewise when the virus attacks the endothelial cells in the brain and spinal cord blood leaks out causing hemorrhage while blood clots form which blocks oxygen delivery and neurologic disease develops. When EHV-1 attacks the brain and spinal cord the disease is called Equine Herpes Myeloencephalopathy or EHM.
  • Several years ago a specific strain of the EHV-1 virus was identified (the neurotropic strain) The particular strain of EHV 1 virus has the ability to multiply at a much higher rate. More virus particles mean more cells can be attacked. We started seeing cases of neurologic disease that were much more severe.
  • When a horse becomes infected with EHV it will first develop a fever. If the neurologic system is attacked by the virus the horse may develop signs of incoordination, stumbling, dribbling urine and it may become unable to stand (paresis). These horses require intensive care to survive and not all horses survive even with intensive care. Due to the highly contagious nature of this virus it is now common for hospitals which have a case to close to all other cases to minimize transmission.
In the most recent outbreak a large number of horses were gathered for a competition. The horses were stabled under one roof sharing a common airspace. The horses had a common area to train and exercise. Once the horses from this competition disbanded and went home to their own stables they took the virus with them. EHV is a highly contagious virus, and as a result of the travel of the exposed horses who left the show a total of 1635 horses were reportedly exposed to the virus. As of this date there have been 88 cases of EHV infection and 33 cases of EHM; 12 horses have died or been euthanized due to severity of neurologic disease.

The Horse magazine has made an excellent webinar on EHV  that I found to be very helpful. Click here

The USDA has been tracking this outbreak, you can get daily updates by clicking here.

For more information about EHV the AAEP has formulated a list of Frequently Asked Questions

Protecting Your Horse
Horses at low risk. Vaccination is not recommended if;
  1. Your horse lives on private property and does not travel.
  2. Other horses on the farm do not leave the property.
  3. Visiting horses do not come on the property.
  4. People making contact with the horse do not visit other horses or barns.

Horses at moderate risk. Vaccination with a killed or modified live vaccine every 6 months is likely to be adequate if;
  1. You occasionally travel with your horse, but your horse does not stay in public stabling.
  2. Your horses lives at a boarding stable where people and horse come and go.

Horses at high risk.Vaccination with the modified live vaccine every 90 days is recommended.
  1. Your horse is traveling to shows or competitions where he is stabled with other horses or stabled in public barns.
  2. Your horse lives in a boarding barn where horses frequently leave for overnight competition
  3. Your horses lives in a boarding stable when visitors frequent that have likely been in contact with horses from other barns, clinics or shows.
  4. Your horse lives on a farm that host clinics or seminars.

Biosecurity for your farm
  • Disease control starts at home. New arrivals to the farm should be quarantined for a minimum of 14 days before they are allowed to have contact with the resident herd. Use separate grooming tools, muck tubs, forks etc for the quarantined horses.
  • When you are at shows or events you should wash your hands especially after handling other horses.
  • Donít let your horse touch other horses especially nose to nose.
  • Donít share equipment especially buckets.
  • Donít allow community hoses to drop into your water buckets.
For more tips on biosecurity check out this helpful link.

Finally, the more you know about EHV the better equipped you will be to protect your horse. I know this is a tough subject, certainly not light reading. I hope that this information will help you to understand this virus and the tools available to help protect your horse.